The evolution of modern electronics enables complex circuitry to be reduced to increasingly miniaturized, packing increasingly larger numbers of active devices into a square millimeter. Just as miniaturization is bound by physical laws, so are other aspects controlling how small devices may be made.
Two key areas affecting device miniaturization involve communications with other devices, and powering the device itself. Micropower digital and analog circuit design enables devices to be powered by photovoltaic cells covering a few square centimeters.
As much as designers would like to shrink the size of a device, physical laws still require that for efficient radio frequency (RF) communications, the size of an antenna is related to the wavelength of interest. As an example, many antenna designs require elements on the order of a quarter wavelength of the operating frequency.